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United States Patent |
5,515,750
|
Green
|
May 14, 1996
|
Formation of tools for producing threads with varying pitch
Abstract
A method of forming a threading tool for producing a thread of varying
pitch in a work piece by relative rotary and axial movement between the
tool and work piece. The tool is constructed to have a series of threading
projections including a first series of pre-forming projections for
initially producing a partial thread and groove in the work piece, and one
or two final projections for reshaping the partial thread to have the
varying pitch. The projections may be formed in two or more steps,
including a first step of initially shaping both the pre-forming and final
projections to an initial form, and a subsequent step of then removing
material from one axial side of the pre-forming projections in a relation
giving them a reduced axial thickness less than that of the final
projection or projections, and to an extent such that, upon relative
rotary and axial movement betwee- the tool and work piece, the preforming
projections will at all times remain within the axial sectional profile of
the thread groove of varying pitch ultimately formed by the final
projections.
Inventors:
|
Green; William P. (3570 E. Lombardy Rd., Pasadena, CA 91107)
|
Appl. No.:
|
155127 |
Filed:
|
November 12, 1993 |
Current U.S. Class: |
76/117; 470/198 |
Intern'l Class: |
B23G 005/06 |
Field of Search: |
470/198,199,204,96
409/65
76/117
|
References Cited
U.S. Patent Documents
1542893 | Jun., 1925 | Kreutzberger | 470/198.
|
1543007 | Jun., 1925 | Hanson | 470/198.
|
1770585 | Jul., 1930 | Steinruck | 470/198.
|
1874378 | Aug., 1932 | Steinruck | 470/199.
|
1912517 | Jun., 1933 | De Lapotterie | 470/198.
|
1982737 | Dec., 1934 | Judge | 470/198.
|
1982738 | Dec., 1934 | Judge | 470/198.
|
2307680 | Jan., 1943 | Hohwart | 470/198.
|
2737670 | Mar., 1956 | Conner | 470/198.
|
3125772 | Mar., 1964 | Beck | 470/198.
|
3251080 | May., 1966 | Sharon | 470/198.
|
3355752 | Dec., 1967 | Haralampiev et al. | 470/198.
|
4181457 | Jan., 1980 | Holmes | 470/198.
|
4842464 | Jun., 1989 | Green.
| |
4956888 | Sep., 1990 | Green.
| |
5086532 | Feb., 1992 | Green.
| |
5112168 | May., 1992 | Glimpel | 470/198.
|
Foreign Patent Documents |
2611154 | Aug., 1988 | FR | 470/198.
|
2627408 | Aug., 1989 | FR | 470/198.
|
1-289615 | Nov., 1989 | JP | 470/198.
|
1389955 | Apr., 1988 | SU | 470/198.
|
Other References
"Tool Engineers Handbook--2nd Edition" by ASTME Publications Committee
published 1959, pp. 46-1 to 46-41.
The Book "Practical Machine Shop" by John E. Neely, pp. 83 to 90 and 415 to
417.
"Machine Tools Processes and Applications" by Heineman and Genevro, pp. 42
to 46 and 210 to 212.
"Machine Shop Operation and Setups" by Lascoe, Nelson & Porter, pp. 64
through 69, shows and describes conventional.
|
Primary Examiner: Sipos; John
Assistant Examiner: Schoeffler; Thomas C.
Attorney, Agent or Firm: Green; William P.
Parent Case Text
This application is a continuation-in-part of U.S. patent application Ser.
No. 7/904,499 filed Jun. 25, 1992 on "Formation of Threads With Varying
Pitch", now U.S. Pat. No. 5,316,520.
The invention relates to the manufacture of tools for forming threads of
varying pitch in a work piece.
Claims
I claim:
1. The method of producing a threading tool that comprises:
forming on a tool body, by relative rotary and axial movement between the
tool body and tool shaping means, a series of pre-forming projections for
initially producing a partially formed thread and groove in a work piece
by relative rotary and axial movement between the tool body and work
piece, and either one final projection or two final projections operable
by further relative rotary and axial movement of the tool body and work
piece at a varying rate of axial advancement per revolution to
simultaneously engage corresponding portions of two flank surfaces at
opposite sides of a portion of said partially formed thread or at opposite
sides of a portion of said partially formed groove, and to reshape said
corresponding portions of both of said flank surfaces simultaneously to a
predetermined varying pitch, thereby converting said partially formed
thread and groove to a final thread and final thread groove of varying
pitch having a predetermined axial sectional profile;
said method including making said pre-forming projections small enough,
during said formation thereof, to enable said pre-forming projections,
upon relative rotary and axial movement between said body and work piece
at said varying rate in forming a thread of varying pitch, to remain
within the axial sectional profile of the final thread groove of varying
pitch ultimately formed by said final projection or projections, and
thereby avoid interference with said simultaneous reshaping of said flank
surfaces to said varying pitch by said final projection or projections.
2. The method of claim 1, including first producing said pre-forming
projections with excessive axial thicknesses which would not remain within
the axial sectional profile of said final thread groove of varying pitch,
and then removing material from said pre-forming projections to reduce
their axial thicknesses.
3. The method of claim 1, in which said forming of the projections includes
initially shaping the material of both the pre-forming and final
projections to have similar configurations at a predetermined axial side
of the pre-forming and final projections, and then removing material from
said side of the pre-forming projections but not as deeply if at all from
the corresponding side of the final projection or projections, and to an
extent enabling the pre-forming projections to at all times remain within
the axial sectional profile of said final thread groove of varying pitch
during a threading operation.
4. The method of claim 3, in which said material removed from said
pre-forming projections is removed from sides thereof which are trailing
sides in a threading operation.
5. The method of claim 1, in which said forming of the projections includes
initially producing both the preforming and final projections to have a
same axial sectional profile, and then removing material from a side of
the pre-forming projections but not as deeply if at all from the
corresponding side of the final projection or projections to avoid
interference by the pre-forming projections with the shape of the thread
and groove of varying pitch formed by the final projection or projections.
6. The method of claim 1, in which said forming of the projections includes
shaping surfaces of a plurality of the projections at a first axial side
thereof, by relative rotary and axial movement of the tool body and
shaping means, in a relation causing said surfaces to converge toward, and
be disposed at a different lead angle than, surfaces at the opposite axial
side thereof.
7. The method of claim 6, in which said surfaces are given said different
lead angle by alternately increasing and decreasing slightly a rate of
relative axial advancement per revolution of the tool body and shaping
means during formation of said surfaces.
8. The method of claim 1, in which there are two of said final projections
to simultaneously form opposite side surfaces of said thread of varying
pitch in a work piece.
9. The method of claim 1, including first producing said pre-forming
projections with excessive axial thicknesses which would not remain within
the axial sectional profile of said final thread groove of varying pitch,
and then removing material from said pre-forming projections to reduce
their axial thicknesses, said forming of the projections including shaping
surfaces of a plurality of said projections at at least one axial side
thereof by relative rotary and axial movement of the tool body and shaping
means at alternately increasing and decreasing rates of axial advancement
per revolution in a relation causing said surfaces to converge toward, and
be disposed at a different lead angle than, surfaces at the opposite side
of the same projections.
10. The method of claim 9, including shaping said pre-forming projections
so that, as they approach said final projection or projections, each
successive pre-forming projection has an axial thickness slightly greater
than the preceding pre-forming projection.
11. The method of claim 1, including shaping said pre-forming projections
so that, as they approach said final projection or projections, each
successive pre-forming projection has an axial thickness slightly greater
than the preceding pre-forming projection.
12. The method of claim 1, in which said forming of the projections
includes making a series of deepening cuts on the tool body sequentially
forming flank surfaces at one axial side of said pre-forming and final
projections, and making a different series of deepening cuts in the tool
body sequentially forming flank surfaces at the other axial side of said
pre-forming projections.
13. The method of claim 12, including alternately increasing and decreasing
the rate of relative axial advancement per revolution of said tool
body-and shaping means, during one of said series of cuts, in a relation
causing the flank surfaces at one axial side of the projections to
converge toward, and be disposed at a different lead angle than, the flank
surfaces at the opposite axial side of the projections.
14. The method of claim 13, including controlling one of said series of
cuts so that, as said pre-forming projections approach said final
projection or projections, each successive pre-forming projection has an
axial thickness slightly greater than the preceding pre-forming
projection.
15. The method of claim 12, including controlling one of said series of
cuts so that, as said pre-forming projections approach said final
projection or projections, each successive pre-forming projection has an
axial thickness slightly greater than the preceding pre-forming
projection.
Description
BACKGROUND OF THE INVENTION
U.S. Pat. Nos. 4,842,464, 4,956,888 and 5,086,532 disclose a novel type of
nut having a thread of varying pitch which acts to distribute the axial
load applied to the nut more uniformly between the different turns of the
thread than is possible with a conventional thread whose pitch does not
vary. These patents show methods and apparatus for manufacturing such nuts
by employment of lathe type threading tools having a single point which
takes a series of cuts in the work piece, or a similar tool having two
projections for simultaneously forming opposite side surfaces of the
thread. U.S. Pat. No. 5,250,007 shows another method of forming a thread
of varying pitch, utilizing a threading assembly consisting of several
thread forming elements which rotate and advance axially relative to the
work piece essentially in unison, and which also shift axially relative to
one another during a threading operation in a manner producing together
the desired thread of varying pitch.
SUMMARY OF THE INVENTION
The present invention provides improved methods for manufacturing threading
tools capable of producing threads of varying pitch in a simpler and less
expensive manner than in the above discussed prior patents. A tool formed
in accordance with the invention can produce a thread of varying pitch by
a process approximately as simple and inexpensive as conventional tapping
or die cutting operations for producing threads of uniform pitch. The tool
is also essentially as versatile as conventional taps and dies with
respect to the diameter of thread which may be produced.
In manufacturing a threading tool by a method embodying the invention, a
series of threading projections are formed on the tool body by relative
rotary and axial movement between the tool body and a cutting or shaping
element. These projections include a number of pre-forming projections for
initially producing a partial thread and groove in a work piece by
relative rotary and axial movement between the tool body and work piece,
and either one or two final projections operable to give the partial
thread and groove a predetermined varying pitch by further rotary and
axial movement. During the re-shaping action of the final projection or
projections, the tool body and work piece are advanced relative to one
another at a varying rate of axial advancement per revolution, to give the
thread its desired varying pitch.
The method of formation of the tool includes removing enough material from
the pre-forming projections to enable them, upon relative rotary and axial
movement between the tool body and a work piece, to always remain within
the axial sectional profile of the final thread groove of varying pitch
ultimately formed by the final projection or projections to thereby avoid
interference by the pre-forming projections with the shape of the final
groove.
The pre-forming projections may initially be cut to a thickness slightly
greater than their final thickness, with a controlled amount of material
then being removed from one or both sides of each projection to give them
a reduced size which will not interfere with the groove of varying pitch
ultimately produced by the final projection or projections. In one method
embodying the invention, both the pre-forming and final projections may
initially be cut to the same axial sectional configuration, with material
then being removed from a side of the pre-forming projections but not as
deeply if at all from the final projection or projections to arrive at the
final configuration of the tool. Also, at some point during the tool
manufacturing process, surfaces at one side of at least some of the thread
forming projections, as viewed in axial section, may be shaped to converge
circularly toward and be disposed at a different lead angle than
corresponding surfaces at the opposite sides of the projections, to enable
the projections to effectively cut a work piece during a threading
operation.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other features and objects of the invention will be better
understood from the following detailed description of the typical
embodiments illustrated in the accompanying drawings, in which:
FIG. 1 is a diagrammatic representation of apparatus for producing an
internal thread of progressively increasing pitch within a nut body, and
including a tapping tool which may be formed by the methods of the present
invention;
FIG. 2 is an enlarged transverse section through the tapping tool of FIG.
1, taken on line 2--2 of that figure;
FIG. 3 is a greatly enlarged view taken on line 3--3 of FIG. 2, with the
tapping tool shown after it has advanced into the nut body;
FIG. 4 is a view similar to FIG. 3, but showing the thread in the nut body
after the tapping tool has moved entirely through the nut body and the
thread of increasing pitch has been completely formed;
FIG. 5 is an enlarged fragmentary view corresponding to the left hand
portion of FIG. 3, but with the tapping tool illustrated as it appears
after it has been advanced rightwardly one full turn beyond the position
of FIG. 3;
FIG. 6 is an enlarged fragmentary view showing the right end turn of the
completely formed thread of FIG. 4, with illustration on the figure of the
cuts of the various pre-forming projections of the tapping tool;
FIG. 7 is an enlarged fragmentary section taken on line 7--7 of FIG. 3;
FIG. 8 is a fragmentary view similar to FIG. 3, and showing a variational
form of threading tool;
FIG. 9 is an enlarged diagrammatic view showing the cuts made in the right
hand thread groove of FIG. 8 during the first portion of a threading
operation utilizing the tool of FIG. 8;
FIG. 10 is a fragmentary view similar to FIGS. 3 and 8 of another
variational type of threading tool;
FIG. 11 is a fragmentary view corresponding to a portion of FIG. 1 and
showing another form of threading tool;
FIG. 12 represents diagrammatically a process embodying certain features of
the invention and utilizing two separate threading tools;
FIG. 13 illustrates diagrammatically a process for manufacturing the
threading tool of FIGS. 1 to 7;
FIG. 14 is an enlarged axial section through a portion of the apparatus of
FIG. 13 and illustrating three steps in the preferred process of forming
the threading tool; and
FIG. 15 is a fragmentary view taken partially on line 15--15 of FIG. 14 and
developed circularly about the axis of the tool being formed.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates diagrammatically at 10 apparatus embodying the invention
for forming an internal thread of progressively increasing pitch within a
cylindrical bore 11 in a nut body 12. The thread is produced by moving the
nut body and a threading tool 16 both rotatively and axially relative to
one another in timed relation. Any type of lathe, threading machine, screw
machine or other machine tool capable of producing such relative movement
may be employed. For example, the nut body may be held by a chuck 13 of a
lathe or other tool, with the chuck being mounted for powered rotation
with the nut about axis 14. A tool holder 15 may carry the tapping tool
16, centered about axis 14, and be mounted for controlled movement along
axis 14 toward and away from chuck 13. Computer controlled driving
mechanism diagrammatically represented at 17 may rotate chuck 13 and the
nut about axis 14, and move tool holder 15 and tap 16 along axis 14 in
timed relation to the rotation of the nut. The drive connections from
mechanism 17 to chuck 13 and tool holder 15 are diagrammatically
represented at 18 in FIG. 1.
Instead of rotating the nut and moving the tool 16 axially, these motions
may of course be reversed if desired, with tool holder 15 and tap 16 being
driven rotatively but not axially, and with the chuck 13 and work piece 12
being shifted axially but not driven rotatively. Also, either the tapping
tool or nut may be driven both rotatively and axially, or both may have
each of the two types of motion, so long as the desired relative axial and
rotary movement between the tapping tool and work piece as discussed
hereinafter is attained.
Tapping tool 16 may be formed as a one piece body of tool steel or other
hardened material capable of cutting a thread within the interior of nut
12 without damage to the tapping tool. The tapping tool may-have a shape
very similar to a conventional thread cutting tap, being elongated in a
left to right direction as viewed in FIG. 1, and having a mounting portion
19 adapted to be gripped and held by tool holder 15. Rightwardly of the
tool holder 15 in FIG. 1, the tapping tool 16 may have the cross section
illustrated in FIG. 2, typically forming four radially outwardly
projecting portions 20a, 20b, 20c and 20d carrying outwardly projecting
cutting teeth 21, with recesses or flutes 22 formed circularly between the
portions 20a, 20b, etc. for reception of lubricant, cooling fluid and
cuttings removed from the work piece. In lieu of the arrangement
illustrated in FIG. 2, with the four outwardly projecting cutter carrying
portions of the tap body, that body may of course have more or less than
four such portions as is well known in the threading art. The cross
section illustrated in FIG. 2 is uniform along the entire length of the
active threading portion of the tapping tool, from its extremity 23 to the
location 24 in FIG. 1. Leftwardly of that location, the body of tapping
tool 16 may be externally cylindrical, square, or of any other cross
sectional configuration capable of being effectively gripped and held by
chuck 15. When the thread to be formed in nut body 12 is a right hand
thread, portion 20a of tool 16 is the first of the four portions of the
tool to engage any particular part of the nut body during a threading
operation, followed by portions 20b, 20c and 20d in that order.
The thread cutting projections 21 at the top of FIGS. 1 and 2 are
represented in greatly enlarged form in FIG. 3. These projections include
a number of pre-forming projections 21c, 21d, 21e, 21f, 21g and 21h which
partially shape the thread in the nut body, and two final shaping
projections 21a and 21b at the left end of FIG. 3 which give the thread
its desired ultimate increasing pitch configuration. To describe first of
all the action of the final projections 21a and 21b, these two projections
have the thread shaped axial cross section illustrated in FIG. 3, for
forming a similarly shaped thread 25 in the interior of nut body 12, as
chuck 13 and nut body 12 are rotated about axis 14, and as tool 16 is
simultaneously advanced rightwardly along that axis. Thread 25 formed by
projections 21a and 21b preferably has the outline configuration of a
standard sixty degree thread, defined by a trailing flank surface 26, a
leading flank surface 27, and an axially extending crest surface 28. In
the position of FIG. 3, surfaces 26 and 27 are being cut to the
illustrated shape by a cutting edge 29 at the leading side of projection
21a, and a cutting edge 30 at the trailing side of projection 21b, with
these edges 29 and 30 (and the formed surfaces 26 and 27) being disposed
at a sixty degree angle to one another. A third cutting edge 31 extending
axially between projections 21a and 21b forms the crest surface 28 of the
produced thread,
The pre-forming projections 21c through 21h of FIG. 3 are smaller than
projections 21a and 21b and act to partially form the thread groove in the
nut body before the final shaping process by projections 21a and 21b. In
FIG. 3, six such pre-forming projections are typically illustrated, though
it will be understood that more than six or less than six may be employed.
The first of these projections to contact the work piece during a
threading operation is the right end projection 21h, which as illustrated
is relatively short radially to make an initial shallow cut in the nut
body. Projection. 21g has a somewhat greater radial dimension, to make a
deeper cut, and the remaining projections 21f, 21e, 21d, and 21c
successively deepen the inter-thread groove in the nut body before the
final shaping operation by projections 21a and 21b.
The cutting projections 21a through 21h described above and shown in FIG. 3
are all formed on portion 20a of the tapping tool 16 (see FIG. 2). Each of
the other three portions 20b, 20c and 20d of the tapping tool has a series
of pre-forming projections corresponding to projections 21c through 21h of
FIG. 3, but does not have the final shaping projections 21a and 21b. The
projections 21c through 21h of the four portions 20a, 20b, etc. of the
tapping tool 16 may be given their progressively increasing radial
dimensions by machining these projections to have outer tapering conically
curving surfaces 32 centered about axis 14. This conical truncation of the
pre-forming projections may be such that the final pre-forming projection
21c of portion 20d of tool 16 (that is, the last preforming projection to
engage any particular portion of the nut body before projection 21b
contacts that portion of the nut) is not truncated at all and has a full
radial height corresponding to that of projections 21a and 21b.
The projections 21c through 21h of portion 20b of the tapping tool are
shifted slightly in a leftward direction (leftward as viewed in FIGS. 1
and 3) relative to the corresponding teeth 21c through 21h of portion 20a
of the tool because of the ninety degree offset of portions 20a and 20b
relative to one another about axis 14. This leftward shift causes each of
the pre-forming projections 21c through 21h of portion 20b of the tapping
tool to project slightly farther radially outwardly than the corresponding
projection of portion 20a as a result of the conical truncation of all of
the projections at 32. Similarly the cutting projections of portion 20c
are shifted farther to the left in FIG. 3, and have a greater radial
dimentsion, than the corresponding projections of portion 20b, and the
projections of portion 20d are shifted leftwardly farther to the left, and
extend farther out radially than the projections of portion 20c. Thus, the
projections 21c through 21h of the four portions of the tapping tool all
lie along an essentially helical path enabling the projections of the
various portions 20a, 20b, 20c and 20d to sequentially engage and cut any
particular portion of the nut body during a threading operation and
thereby form an essentially helical thread groove in the nut body in a
manner similar to a conventional tapping tool. The helix defined by all of
these projections 21c through 21h is of uniform pitch from the right end
of the tapping tool through all of these cutting edges. Also, projections
21a and 21b may be considered as lying along essential the same uniform
pitch helical path.
As an aid in understanding the preferred relationship between the
configuration of cutting projections 21c through 21h of FIG. 3 and the
final precise shaping teeth 21a and 21b, FIG. 3 includes reference lines
33c through 33h representing in broken lines a uniform pitch continuation,
of the thread pattern defined by projections 21a and 21b. For example, the
lines 33c immediately to the right of projection 21b define a thread
shaped profile having the same axial sectional outline configuration as
projection 21a and projection 21b, and spaced from projection 21b a pitch
distance p which is equal to the pitch distance p between projections 21a
and 21b. Similarly, the lines or pattern 33d are spaced that same distance
from lines 33c, and the other reference lines 33e, 33f, 33g and 33h are
all spaced apart the same uniform pitch distance.
The leading cutting edge 34 of each of the projections 21, 21d, 21e, 21f,
21g and 21h preferably coincides with the angularly disposed line 134
defining the leading side of the corresponding broken line reference
pattern 33c, 33d, 33e, 33f, 33g or 33h. The cutting edges 35 at the
trailing sides of projections 21c, 21d, 21e, 21f, 21g and 21h, however, do
not coincide with the angularly disposed lines 36 of the reference
patterns 33c, 33d, 33e, etc., but are parallel to lines 36 and spaced
rightwardly a substantial distance relative thereto. This leaves a portion
37 of the nut body to the left of each of the cutting projections 21c
through 21h, which allows for the slight increase in pitch of the thread
ultimately to be formed in the nut body by the final shaping projections
21a and 21b.
To now describe a cycle of operation of the apparatus of FIGS. 1 to 7,
assume that cutting tool 16 is positioned within holder 15 as shown in
FIG. 1, and is initially in the position of that figure just to the left
of nut body 12. The nut body may at the outset have a bore 11 of a
diameter corresponding to or slightly less than that of the minor diameter
cutting edges 31 of the threading tool. The nose portion 38 of the tapping
tool 16 may have a slight conical taper about axis 14, and be a close fit
within bore 11 to assist in centering the tapping tool within the nut
body. To perform a tapping operation, the drive mechanism 17 is actuated
to commence rotation of chuck 13 and nut body 12 about axis 14 at a
predetermined rate, and to commence programmed axial movement of tool
holder 15 and tapping tool 16 in a rightward direction in predetermined
timed relation to the rotation of the nut body. During an initial portion
of the threading operation, as tapping tool 16 advances rightwardly from
the position of FIG. 1 just outside nut body 12 to the position of FIG. 3,
the axial advancement of tapping tool 16 rightwardly relative to nut body
12 may be at a uniform rate, advancing tool 16 exactly the pitch distance
p of FIG. 3 during each revolution of the nut body. As a result, the
pre-forming cutting projections 21c through 21h of the four portions 20a,
20b, 20c and 20d of the tapping tool progressively form and deepen a
helical thread groove of uniform pitch in the nut body. When the FIG. 3
position is reached, the portion of the nut body which is then in contact
with projection 21c of portion 20a of the tool is being cut by that
projection to a cross section corresponding to that of the illustrated
projection 21c. The corresponding projections 21c of the other three
portions 20b, 20c and 20d of the tool are at the same time cutting the nut
body to a slightly greater radial depth, giving the groove an ultimate
major diameter the same as the major diameter of an outer cutting edge 230
of projection 21b.
When the tool reaches a point at which the final shaping teeth 21a and 21b
are commencing their cutting operation in the work piece, such as the
position illustrated in FIG. 3. or a slightly earlier position, the
computer controlled mechanism 17 automatically converts to a changed
condition in which, instead of advancing the threading tool rightwardly at
a uniform rate per revolution, the tool is advanced rightwardly at a
progressively increasing rate per revolution. In a nut of the type
disclosed in U.S. Pat. No. 3,842,464, that increase in the rate of
advancement, and the resultant increase in pitch in the thread formed in
the nut body, are relatively slight, typically being on the order of one
tenth of one thousandth of an inch per revolution for certain thread sizes
such as 5/8.times.16. In order to make this advancement visible in the
drawings, the advancement has been exaggerated.
FIG. 5 represents the positions of the final cutting projections 21a and
21b after they have advanced through one complete revolution of the nut
body from the position of FIG. 3. FIG. 4 shows the completed thread in the
nut body after all of the cutting projections 21a through 21h of tool 16
have advanced entirely through the nut. Reference lines 33c, 33d, etc. and
the FIG. 3 positions of the cutters have been included in FIG. 4 to assist
in understanding the thread cutting action.
When the nut body and tool 16 are in their FIG. 3 positions (or a slightly
earlier position if preferred) the rate of relative axial advancement of
the threading tool and nut, and the resultant lead angle of the portion 71
of the thread then being formed, correspond to the pitch distance p
between projections 21a and 21b. That is, in the FIG. 3 position the tool
16 and nut body are advancing axially relative to one another at an
instantaneous rate and lead angle and effective pitch which would advance
these parts axially through the distance p in one revolution if the rate
of advancement did not increase. In this connection, the "effective pitch"
of the relative motion and formed thread at any particular point is
defined as the distance which the thread would advance axially from that
point during a single revolution if the rate of advancement did not
change. The "effective pitch" in the FIG. 3 position is therefore the
distance p.
During one revolution of the nut body from the FIG. 3 position, the rate of
relative axial advancement of the tool and nut body progressively
increases slightly so that, by the time projection 21b reaches its FIG. 5
position, it does not coincide with the previously mentioned reference
lines 33c, but is shifted slightly to the right relative thereto.
Similarly, the projection 21a does not, at the end of the first
revolution, coincide in position with the FIG. 3 position of projection
21b at the commencement of that revolution, but is shifted rightwardly
relative thereto (shift exaggerated in FIG. 5). As a result, the trailing
cutting edge 30 of projection 21b and the leading cutting edge 29 of
projection 21a, and the axially extending edge 31 therebetween, form a
second turn 72 of the thread in the nut which is shifted slightly in a
rightward direction relative to the uniform pitch reference lines 33c and
thus has an increased lead angle and effective pitch greater than the
starting pitch p. In FIG. 5, the FIG. 3 position of the leading edge 29 of
projection 21 b is represented at 129. The trailing edge 40 of projection
21a is in FIG. 5 spaced slightly from the surface 27 previously formed by
edge 30 of the projection 21b.
During the next revolution of the nut body and tapping tool relative to one
another, the rate of axial advance of the tapping tool continues to
increase at the same uniform rate, so that the third turn 73 of the thread
is shifted farther to the right relative to reference patterns 33c and
33d, as represented by the spacing at 78 in FIG. 7. Similarly, the fourth
turn 74 is shifted still farther, as represented at 79, and each of the
other turns 75, 76, 77 and 78 is shifted farther than the preceding turn
(see spacing at 80, 81, 82 and 83). The shift is never great enough,
however, to permit the cuts previously made by pre-forming projections 21c
through 21h to interfere with the shape of the ultimate increasing pitch
groove formed by projections 21a and 21b. This is true because of the
reduced width of each projection 21c through 21h as represented at 37 in
FIG. 3. The right flank surfaces 183 of the thread turns do not reach the
lines 84 of FIG. 4 which define the cuts made in FIG. 3 by the left
cutting edges 35 of pre-forming cutters 21c, 21d, etc. The axial dimension
of the inter-thread groove in FIG. 4 gradually increases at each turn (in
a rightward direction), while the axial cross section and axial thickness
of the formed thread itself remain uniform. In this way, the desired
thread of progressively increasing pitch is formed in the nut. The thread
cutting operation performed by projections 21a and 21b is similar to that
performed by the two projections or teeth of the threading tool 54 shown
in FIGS. 10 and 11 of U.S. Pat. No. 4,842,464.
All of the various cutting projections 21a, 21b, 21c, etc. of the threading
tool 16 are relieved circularly behind their cutting edges in a manner
permitting those edges to properly engage and cut the material of the nut
body at the different lead angles and effective pitches at which the
cutting projections move relative to the nut body during formation of the
thread of increasing pitch. This feature is illustrated in FIG. 7, which
shows a portion of the cutting projection 21b of FIG. 3 in cross section.
The cutting edges of that projection 21b are at the lower end of the
projection as viewed in FIG. 7, and include the previously mentioned
cutting edge 30 at the left side of projection 21b, a cutting edge 130 at
the right side of the projection, and an axially extending cutting edge
230 (visible in FIG. 3 but not in FIG. 7) for forming the root portion of
the thread groove in the nut body. These three cutting edges define the
thread profile illustrated in FIG. 3, corresponding to that of a standard
sixty degree thread. The opposite side surfaces 48 and 49 of cutting
projection 21b circularly behind cutting edges 30, 130 and 230 have a
similar sixty degree profile approximately the same as the cutting edges,
but with the axial thickness of that profile gradually reducing toward the
trailing end 50 of the cutting projection, as represented by the fact that
the surfaces 48 and 49 gradually converge in FIG. 7 from their leading
ends to their trailing ends. This tapering of the cutting projection is
such that surface 49 at the right side of the projection is disposed at a
lead angle at least as great as, and preferably slightly greater than, the
maximum lead angle at which projection 21b and the nut body move relative
to one another during a threading operation, that is, the maximum lead
angle of the thread formed in the nut body. The maximum lead angle of the
thread of course occurs at the right end of the nut in FIG. 3. The
opposite side surface 48 of projection 21b is disposed at a lead angle at
least as small as, and preferably slightly smaller than, the minimum lead
angle at which projection 21b moves relative to the nut body, and the
resultant minimum lead angle of the formed groove in the nut body, at the
left end of that body. This relationship permits the cutting edges to
properly engage and cut the material of the nut body at all times during
the thread cutting operation, without interferance surfaces 48 and 49, and
in spite of the fact that the rates of axial advancement of the cutting
tool and the formed thread per revolution vary during that operation.
While FIG. 7 illustrates the tapered shape of only the single cutting
projection 21b, it will be understood that all of the other cutting
projections are similarly tapered, with the same relationship between the
lead angles of their opposite side surfaces and the maximum and minimum
lead angles of the tool and nut relative motion and resulting thread.
FIG. 6 illustrates in enlarged form the final configuration of the right
hand end portion of the thread groove 41 in the nut body as viewed in FIG.
4. In FIG. 6, the cut made by projection 21h is represented in broken
lines at 121h, and the cuts made by projections 21g, 21f, 21e, 21d and 21c
are represented in broken lines at 121g, 121f, 121e, 121d and 121c,
respectively. Each of these cuts is shifted slightly to the right relative
to the preceding cut, by reason of the fact that there is an increase in
the rate of axial advancement of the threading tool beyond the FIG. 3
position of that tool. The final cut made by edge 29 of projection 21a, to
form the right wall 45 of the thread groove, eliminates the irregularity
formed in that wall of the groove resulting from the rightward shift of
the cuts made by projections 21c, 21d, etc.
It is particularly noted in FIG. 6, as previously pointed out with respect
to FIG. 4, that the reduced axial thicknesses of cutting projections 22c
through 22h, and the cuts 121c through 121h made thereby, resulting from
the discussed spaced relationship at 37 in FIG. 3, allow those projections
and their cuts to at all points along their path of movement relative to
the nut body fall within the axial sectional profile of the inter-thread
groove 41 of varying pitch ultimately formed in the work piece, None of
the cuts 121c through 121h of FIG. 6 is wide enough to interfere with wall
44 or 45 or high enough to interfere with upper surface 46 of the groove,
thus permitting the final projections 21a and 21b to give the thread its
ultimate shape. This is true at all points along the entire generally
helical extent of the formed thread. A drawing along the lines of FIG. 6
could be produced for any desired point along the length of the thread.
In the threading process as thus far described, it is assumed that the
threading tool 16 is advancing axially relative to nut body 12 at a
uniform rate per revolution until it reaches the position illustrated in
FIG. 3, and is then advanced at a progressively and uniformly increasing
rate per revolution until all of the cutting projections have moved
entirely through the nut body and completed their threading operation. As
a variation of the invention, the threading tool may be advanced at an
increasing rate through the entire threading process, that is, from a
point prior to initial engagement of the cutting tool with the left end of
the nut body to the point at which all of the cutting projections of the
tool have moved through the nut body and out of contact with it at its
right side. FIG. 8 illustrates a tool 51 which may be utilized in this
manner. The threading tool 51 may be identical with tapping tool 16 as
illustrated in FIG. 3 except that the six preforming projections 52c, 52d,
52e, 52f, 52g and 52h of FIG. 8 (corresponding to projections 21c, 21d,
21e, 21f, 21g and 21h of FIG. 3) are cut away slightly at their leading
sides (right sides in FIG. 8) as well as their trailing sides. To assist
in understanding this feature, FIG. 8 includes the same uniform pitch
thread shaped reference lines or patterns 33c, 33d, 33e, 33f, 33g and 33h
as in FIG. 3. In FIG. 3, the leading cutting edge 34 of each of the
pre-forming projections 21c, 21d, etc. coincides with the angularly
disposed line 134 defining the leading side of the corresponding reference
pattern 33c, 33d, etc. In FIG. 8, the leading cutting edges 53
(corresponding to edges 34 of FIG. 3) do not coincide with the inclined
lines 134, but instead are parallel to those lines and spaced leftwardly
therefrom, in a manner similar to the previously described spaced
relationship at the left sides of the cutting projections, as discussed in
connection with FIG. 3. This relief of the cutting projections at their
right sides in FIG. 8 enables those projections, during axial advancement
of the tool before reaching the FIG. 3 position, to at all times remain
entirely within the axial sectional profile of the increasing pitch thread
ultimately formed in the nut body, and thus prevent the cutting
projections 52c , 52d, etc. from interfering with proper formation of the
opposite side walls of the thread groove. It will of course be understood
that the left end of the threading tool 51 of FIG. 8 includes two thread
cutting projections identical with the projections 21a and 21b of FIG. 3
and having the same relationship to reference patterns 33c, 33d, etc. as
in FIG. 3, The projections 21a and 21b have been omitted in FIG. 8 to
simplify the drawing.
FIG. 9 illustrated diagrammatically the manner in which the axial
advancement of threading tool 51 of FIG. 8 is controlled to maintain the
various pre-forming cutting projections 52c, 52d, etc. within the profile
of the ultimate thread groove formed in the nut body during the initial
advancement of the tool up to a position corresponding to that of FIG. 3.
When the tool of FIGS. 8 and 9 is in a position corresponding to or
slightly to the left of that shown in FIG. 3, in which position the final
thread shaping projections 21a and 21b are commencing their threading
operation to produce the ultimate thread of increasing pitch, the tool 51
is at that position being advanced axially relative to the nut at a lead
angle and effective pitch corresponding to pitch p. Consequently, the
portion of the thread then being formed in the nut has that lead angle and
effective pitch. When tool 51 is in a position leftwardly of the FIG. 3
position, such as the position of FIG. 1 just prior to engagement of the
threading tool with the nut body, the tool is being advanced axially in a
rightward direction at a rate and lead angle and effective pitch less than
the rate and lead angle and effective pitch in the FIG. 3 position. From
the position of FIG. 1 to a position corresponding to that of FIG. 3, the
rate of axial advancement of the tool 51 per revolution gradually
increases, preferably at a uniform rate. Beyond the position corresponding
to FIG. 3, the rate of advancement continues to increase, preferably at
that same uniform rate per revolution, until all of the cutting edges have
moved rightwardly beyond the right end of the nut body. During the portion
of this advancement up to the point at which the tool reaches the FIG. 3
position, the various cutting edges 52c, 52d, etc. make cuts in the nut
body which are slightly shifted relative to one another, as represented in
FIG. 9. The thread groove 54 illustrated in that Figure may be considered
as corresponding to the groove 154 which is nearest the left end of the
nut body in FIG. 4.
When the smallest cutting projection 52h of FIG. 8 is in contact with the
nut body 12, at the location illustrated in FIG. 9, projection 52h makes
the cut identified by that number in FIG. 9. Because of the slow rate of
advancement of the threading tool at that point, the cut 52h is shifted
rightwardly, with the result that its right edge 55 is near but does not
reach the plane in which the right hand wall 56 of the ultimate increasing
pitch thread groove 54 is to be formed by the final two thread shaping
projections 21a and 21b. If projection 51h were not cut away at its right
side as illustrated in FIG. 8, the right portion of that projection would
extend rightwardly beyond the planar surface 56 and prevent final
formation of that surface at a proper location. In similar manner, the
projections 52g, 52f, 52e, 52d and 52c make sequential cuts at the
locations represented in FIG. 9. Because of the slow though progressively
increasing rate of advancement of the tool, each of these successive cuts
is shifted slightly to the left of the preceding one as illustrated in
FIG. 9. However, all of these cuts in their entirety always remain within
the profile of the groove 54 ultimately to be formed by the final shaping
projections 21a and 21b. The same is true at all points rightwardly beyond
the location represented in FIG. 9, with the cuts made by the different
cutting projections remaining within the profile of the final groove to be
formed at all locations. After the tool reaches a position corresponding
to that of FIG. 3, the cutting action of the tool 51 of FIG. 8 is
essentially the same as has been described in connection with FIG. 3. It
will of course be understood that the tool of FIG. 8 may if preferred be
operated in accordance with the timing cycle described in connection with
the arrangement shown in FIG. 3, with the tool 51 being advanced axially
at a uniform rate per cycle until a position corresponding to FIG. 3 is
reached, and then being advanced at a uniformly increasing rate while the
final shaping projections 21a and 21b are acting on the nut body.
FIG. 10 illustrates fragmentarily another variational arrangement, in which
the threading tool 57 may be identical with that shown in FIG. 3 except
that the various pre-forming projections represented at 21c, 21d, 21e,
21f, 21g and 21h in FIG. 3 are shaped slightly differently at their
trailing sides. FIG. 10 shows only four of these projections, identified
by the numbers 58c, 58d, 53g and 53h, with the intermediate projections
(corresponding to 21e and 21f of FIG. 3) being omitted to simplify the
drawing. The left edge 59 of the smallest of these projections 58h may be
substantially the same as the left edge of projection 21h in FIG. 3, being
parallel to and spaced a substantial distance rightwardly of the adjacent
portion of reference line 33h. The next larger projection 58g has its left
hand cutting edge 60 slightly closer to its adjacent reference line 33g,
but still parallel thereto. The cutting projections leftwardly of
projection 58g similarly have edges 61 which are parallel to but move
progressively closer to the corresponding reference lines. This change may
be a gradual and progressive change, with the spacing ultimately
disappearing and the cutting edge almost coinciding with the reference
line at the left side of cutter 58c, the last pre-forming cutter which
engages the nut body just prior to its contact with the first of the final
shaping projections 21b.
In utilizing the tool of FIG. 10, the timing procedure described in
connection with FIGS. 3 and 4 may be utilized, to advance the tool 57
axially at a uniform rate per revolution up to the position illustrated in
FIG. 3 with a progressive and uniform increase in the rate of axial
advancement per revolution beyond that FIG. 3 position. The progressive
increase in width of the cutaway regions at the left sides of cutters 58c
through 58h is permissible because the final shaping projections 21a and
21b are shifted only slightly relative to reference lines 33c, etc. near
the left end of the nut body and are shifted much farther relative to the
reference lines as the cutters advance toward the right end of the nut.
FIG. 11 shows another form of threading tool 62 which may be identical with
the tool 16 of FIGS. 1 to 7 except that the final thread shaping
projections 63 and 64, corresponding to projections 21a and 21b of FIG. 3,
are spaced axially from all of the other projections 65, corresponding to
projections 21c, 21d, 21e, 21f, 21g and 21h of FIG. 3, with cylindrically
curved external surfaces 66 formed on the tool axially between the spaced
projections and at a diameter not greater than the minor diameter of the
cutting projections and the thread formed thereby. The space between
projections 64 and 65 is long enough to permit the pre-forming projections
65 to all advance entirely through the nut body 67 and complete formation
of their uniform pitch thread therein before projections 63 and 64 first
contact the nut. The tool 62 is advanced axially at a uniform rate per
revolution while projections 65 perform their pre-forming operation, and
is advanced at a progressively and uniformly increasing rate per
revolution while projections 63 and 64 perform their final shaping
operation, as in FIG. 3.
Some but not all of the advantages of the invention can be attained
utilizing two separate threading tools 68 and 69 as shown in FIG. 12. The
first of these tools has several circularly spaced series of thread
cutting pre-forming projections 70 which may be the same as projections
21c, 21d, 21e, 21f, 21g and 21h of FIG. 3. Tool 68 is advanced both
rotatively and axially at a preferably uniform rate per revolution,
relative to the nut body 12, from the full line position to the broken
line position of FIG. 12, so that projections 70 form a partial thread of
uniform pitch in essentially the same manner as in FIG. 3. The nut is then
moved to a position opposite tool 60, which has two projections 170
corresponding to projections 21a and 21b of FIG. 3, and which is advanced
rotatively and axially relative to and through the nut body at a
progressively and uniformly increasing pitch, in correspondence with the
movement of projections 21a and 21b in FIG. 3 relative to the nut, to give
the thread its final increasing pitch configuration.
The projections 70 of threading tool 68, instead of being shaped in
correspondence with projections 21c, 21d, etc. of FIG. 3, may have any
other shape capable of forming a partial thread groove which will be
contained entirely within the space defined by the inter-thread groove of
increasing pitch ultimately formed by projections 170 of tool 69. For
example, projections 70 may correspond to projections 52c through 52h of
FIG. 8, or projections 58c through 58h of FIG. 10. In this connection, it
is noted that projections 52c through 52h of FIG. 8 have an axial
sectional cutting profile which is essentially the same as an undersize
conventional tap for a standard 60 degree thread. Consequently, in the
process of FIG. 12, the pre-forming tool 68 may be such a standard tapping
tool, of a size designed for tapping of a thread of a pitch diameter
slightly smaller than that of the increasing pitch thread ultimately to be
formed in nut body. This tool will then form a thread groove in the nut
body having a uniform pitch and of reduced axial width because of the
reduced pitch diameter of the tool to lie entirely within the profile of
the final increasing pitch inter-thread groove.
All of the forms of the invention thus far described produce a thread whose
axial thickness and axial cross section remain uniform along the entire
length of the thread, with the groove between successive turns of the
thread progressively increasing in axial width in correspondence with the
increase in pitch of the thread. The uniform cross section of the thread
results because in each instance two thread cutting projections, such as
projections 21a and 21b of FIG. 3, simultaneously form opposite side
surfaces of the thread, such as surfaces 26 and 27 in FIG. 3. It is
contemplated, however, that any of the forms of the invention may be
adapted to produce a thread whose axial thickness increases progressively
while the groove between turns of the thread is of uniform axial width.
This may be accomplished with the FIG. 3 tool, for example, by omitting
its projection 21a, and otherwise constructing and operating the tool as
previously described. Projection 21b then acts by itself as a single point
threading tool to define the unchanging shape of the groove and cause the
increase in thickness of the thread in correspondence with the increase in
the rate of advancement of the tool. The same result can be attained by
omitting the projection corresponding to projection 21a in any of the
other forms of the invention. In each instance, as in the other procedures
previously described, the cuts made by pre-forming projections 21c through
21h always remain within the axial profile of the thread groove of
increasing pitch ultimately formed by projection 21b, and thus do not
interfere with the proper configuration of that groove.
FIGS. 13 through 15 illustrate diagrammatically a process and apparatus for
manufacturing the thread tapping tool 16 of FIGS. 1 to 7. It will be
apparent that similar processes may be employed for producing the other
forms of tapping tools embodying the invention. With reference first to
FIG. 13, there is illustrated at 83 in that Figure a metal body from which
the tapping tool 16 of FIGS. 1 to 7 is to be formed. It is assumed in FIG.
13 that body 83 has already been machined or otherwise formed to the
condition shown in FIG. 1 except for formation of the thread forming
projections 21a through 21h on the body. Mounting portion 19 at the left
end of body 83 is held by a chuck 84 which may rotate tool body 83 about
an axis 85 under the control of a computer actuated drive mechanism 86. A
thread forming tool 87 may be carried by a tool holder 88 which is power
driven axially, that is, parallel to axis 85, under the control of
computer actuated drive mechanism 86, and in timed relation to the
rotation of chuck 84 and tool body 83. Alternatively, any other type of
drive arrangement may be utilized which is capable of producing timed
relative rotary and axial movement between body 83 and cutter 87.
The portion 89 of body 83 which protrudes from chuck 84 may have a cross
section corresponding essentially to that illustrated in FIG. 2 except
that the outer extremities of the four radially outwardly projecting
portions 20a through 20d are unthreaded and have outer cylindrically
curved surfaces 90 centered about axis 85 and of a diameter equal to the
major diameter of the projections 21a, 21b, etc., through 21h ultimately
to be provided on portions 20a, etc. of body 83.
Element 87 may be a conventional thread cutting tool, mounted in holder 88
to project radially inwardly toward axis 85, and having an inner tip
portion 91 (FIG. 14) shaped to have an axial sectional profile
corresponding to that of a standard sixty degree thread, and defined by
cutting edges 92 and 93 at opposite sides of the cutter disposed at a
sixty degree angle with respect to one another. A third cutting edge 94
extending axially between the extremities of edges 92 and 93 forms axially
extending root surfaces 95 in body 83. In lieu of the cutter illustrated
in FIG. 14, element 87 may in certain instances be another type of thread
forming device, such as a thread grinding wheel, thread roller, or the
like.
FIGS. 14 and 15 illustrate diagrammatically three successive steps which
may be performed by thread cutting tool 87 in the outer surfaces of
portions 20a, 20b, etc. of body 83. After completion of these three steps,
a fourth step may be performed by cutter 87 or another cutter to truncate
the pre-forming projections 21c through 21h as represented at 32 in FIG.
3, or if desired that truncating step may be performed before the three
steps illustrated in FIGS. 14 and 15, or between any two of those steps.
The first of the three steps is to form a uniform pitch sixty degree thread
in the outer surfaces of body 83 by rotating that body and simultaneously
advancing tool holder 83 and thread cutting tool 87 axially (preferably
leftwardly in FIG. 14) relative to body 83 at a uniform rate of
advancement per revolution corresponding to pitch p of FIG. 3. This step
is illustrated by the broken line representation of cutter 87 at 87' in
FIG. 14. During such formation of the thread shaped projections on the
outer surfaces of the body 83, the previously mentioned cutting edge 92 of
cutter 87 forms inclined flank surfaces 96 at the rightsides of those
projections, while the opposite cutting edge 93 of cutter 87 forms
surfaces 97 at the trailing sides of pre-forming projections 21c, 21d,
21e, 21f, 21g and 21h, and surfaces 197 at the left sides of the two final
shaping projections 21a and 21b in the left portion of FIG. 14. This
cutting action thus initially forms all of the projections 21a through 21h
to be of the same axial sectional profile and at uniform spacing as in a
standard thread of pitch p. That configuration may of course be produced
by a series of successive cuts in body 83, with element 87 being shifted
slightly radially inwardly between the different cuts to progressively
deepen the thread groove formed in body 83. Leftwardly beyond projection
21a at the left end of FIG. 14, cutter 87 may be controlled to form a
cylindrical surface 198 of a diameter corresponding to minor diameter
surfaces 95 at the roots of projections 21a, 21b, etc.
The second step of the process may be to advance cutter 87 and tool body 83
through another cycle of relative rotary and axial movement, with the
cutter preferably moving leftwardly from the right end of element 83, in a
relation removing material from the left side flank surfaces of preforming
projections 21c through 21h, but not the final shaping projections 21a and
21b. The position of the threading tool 87 relative to the thread groove
during this step is illustrated by the full line representation of cutter
87 in FIG. 14. In that position, the cutting edge 93 at the right side of
element 87, which in the previous step had formed flank surfaces at the
locations 97 in FIG. 14, acts to form surfaces 297 at the left sides of
the projections. These surfaces 297 will ultimately serve as the inclined
left edges 35 of the pre-forming projections of FIG. 3, If the tool to be
formed is of the type shown in FIG. 3, the rate of leftward axial
advancement of element 87 per revolution of the body 83 while the cutter
is in contact with pre-forming projections 21c through 21h is the same
during this second step of the process as during the first step, but with
the axial advancement slightly delayed or offset to the right with respect
to the cycle followed in the first step, so that flank surfaces 297 are
spaced rightwardly of the initially formed surfaces 97 the same distance
for each of the pre-forming projections 21c through 21h. This second step
may if desired be halted before element 87 reaches the two final shaping
projections 21a and 21b on portion 20a of Body 83, so that these
projections 21a and 21b are left with a full thread profile as in FIG. 3.
Alternatively, element 87 may continue its movement past projections 21a
and 21b with the same timing as in the first step, to follow the same path
relative to body 83 as in the first step and in that way leave projections
21a and 21b with their full thread profile.
If the tool to be formed is of the type shown in FIG. 10, rather than that
of FIG. 3, the rate of leftward axial advancement of element 87 per
revolution of body 83 may be slightly greater while cutter 87 is in
contact with projections 21c through 21h during the second step than
during the first step, to progressively reduce the spacing between the
left flank surfaces formed in the second step and surfaces 97 formed in
the first step, and thus gradually and progressively reduce the amount of
material removed from the left flanks of the pre-forming projections 21c
through 21h in the second step. The resulting gradual leftward shift of
the left flank surfaces relative to the positions of the surfaces 297 in
FIG. 14 is represented in FIG. 10 by the gradual reduction in spacing
between edges 59, 60 and 61 of FIG. 10 and the reference lines 33h, 33g,
etc. of that Figure. That spacing is reduced to zero as the cutter 87
reaches projection 21b so that the position of the cutter at that point in
step two coincides with the position of the cutter at the corresponding
point in step one. The cutter may then be advanced past the two final
shaping projections 21a and 21b at a uniform rate corresponding to that of
step one, to follow exactly the same path past projections 21a and 21b as
in step one, and thus leave those projections unchanged by step two. In
lieu of such movement past projections 21a and 21b, the cutter 87 may of
course be halted before reaching those final projections.
A third step in the process of FIGS. 13 to 15 may be performed with cutter
87 again in a position such as that represented in broken lines at 87', to
further shape the right hand flank surfaces 96 of all of the projections
21a through 21h, but with the rate of axial advancement of tool 87 per
revolution of body 83 being alternately increased slightly and decreased
slightly through the entire machining operation to produce surfaces 49 of
increased lead angle on the various projections (see FIGS. 7 and 15).
FIG. 15 is a developed view representing diagrammatically the cuts which
are made during step three on preforming projections 21c through 21h of
the various portions 20a, 20b, 20c and 20d of body 83. The lower portion
of FIG. 15 shows two of the tapping projections 21e and 21f on portion 20a
of body 83, as viewed on line 15--15 of FIG. 14. Above these projections
in FIG. 15, the two corresponding projections 21e and 21f of portion 20b
of the tapping tool are illustrated, and still higher the two projections
21e and 21f of portion 20c are shown. The view is thus developed
circularly about the axis 85 of body 83 and about the corresponding axis
14 of the finished tool illustrated in FIG. 1. The fourth portion 20d of
the tapping tool body has a similar pair of projections 21e and 21f, which
have been omitted from FIG. 15 to simplify the drawing.
The broken lines 99 of FIG. 15 represent the cuts made by tool 87 in the
second step of the above discussed process, in which the cutter is
positioned as shown in full lines at 87 in FIG. 14, that is, while the
right hand cutting edges 93 of element 87 are forming surfaces 297 at the
left sides of projections 21c through 21h of the four portions 20a, 20b,
20c and 20d of the tapping tool. Since the rate of axial advancement of
tool 87 per revolution of body 83 is uniform during formation of the
surfaces 297, the lines 99 appear as straight lines in the developed view
FIG. 15. The broken lines 100 in FIG. 15 represent the final cuts made on
surfaces 96 at the right sides of projections 21a through 21h in the third
step of the process. Because the rate of axial advancement of element 87
per revolution of body 83 alternately increases and decreases during this
step of the process, the lines 100 appear as axially oscillating or waving
lines in FIG. 15. While cutter 87 is in engagement with the right side of
each of the projections 21a through 21h of the four portions of the tool
body 83, the rate of axial advancement of tool 87 per revolution of body
83 is slightly greater than the rate utilized during the first step of the
process in forming the uniform pitch projections at pitch p, so that
surfaces 49 at the right sides of the projections (see also FIG. 7) are
given a greater axial lead than surfaces 297 at the left sides of those
projections. The axial lead of surfaces 49 is as previously discussed at
least as great as and preferably slight greater than the maximum lead
angle of the varying pitch thread to be formed by tapping tool 16 in nut
12 of FIG. 1. After tool 87 has cut this increased lead angle surface 49
on one of the projections, say for example projection 21f of portion 20a
in the lower portion of FIG. 15, the computer controlled drive mechanism
86 acts to automatically slightly reduce the rate of axial advancement of
tool 87 per revolution of body 83, to a rate slightly less than that
associated with pitch p, as represented by a slight curving of the broken
line 100 at 101 in FIG. 15. That reduction in the rate of advancement is
enough to properly position cutter 87 for engagement at 102 with the next
successive projection to be shaped (projection 21f of portion 20b of the
tapping tool), with the rate of advancement then increasing again to form
the increased lead surface 49 at the right side of this second projection.
The rate of axial advancement is alternately increased and decreased in
this same way as cutter 87 successively engages and forms increased lead
surfaces 49 at the right sides of all of the projections 21a through 21h
of portion 20a of the tool, and all of the projections 21c through 21h of
portions 20b, 20c and 20d of the tapping tool. Portions 21b, 21c and 21d
of course do not have the final shaping projections 21a and 21b. The outer
surfaces of these three portions of the tool may be ground away or
otherwise machined or formed to have continuations of the cylindrical
surface 198 at the locations at which projections 21a and 21b of these
three portions of the tool would otherwise be formed.
It is contemplated that the three steps discussed above may be performed in
a different order than has been described or some of those steps may be
combined into a single step or omitted, or altered or supplemented by
other steps. For example, in producing the tool of FIG. 3, the first two
steps may be combined, with the tool 87 acting during a continuous cycle
of axial advancement from right to left in FIG. 14 to first form surfaces
297 on pre-forming projections 21c through 21h, and then form surfaces 197
on projections 21a and 21b. During the first portion of this cycle of
advancement, cutter 87 is in a position relative to the groove
corresponding to the full line position of element 87 in FIG. 14, to form
surfaces 297 on projections 21c through 21h. After cutter 87 moves out of
engagement with the last of the pre-forming projections, the rate of axial
advancement is increased long enough to shift the cutter leftwardly for
proper formation of surfaces 197 on projections 21a and 21b. During actual
formation of those surfaces 197, the rate of axial advancement per
revolution is returned to the same rate as during formation of surfaces
297. It will of course be understood that several passes of the tool may
be made to progressively deepen a series of such continuous cuts made in
the tapping tool, with the cutter 87 being advanced leftwardly at an
increased rate during each of these passes after leaving the last of the
pre-forming projections 21c through 21h, to shift the cutter as discussed.
The first two steps may be similarly combined in forming the tool of FIG.
10, with tool 87 acting during a continuous cycle of leftward advancement
to first form surfaces 59, 60 and 61 of FIG. 10 in the manner previously
discussed, and then on the same cycle form the final projections 21a and
21b. During the formation of surfaces 59, 60 and 61, the tool advances at
a slightly greater rate than during the formation of the final projections
21a and 21b.
After either of the above discussed combined processes of producing all of
the left side flank surfaces 297 and 197 of FIG. 14, or 59, 60, 61 etc. of
FIG. 10, in a single procedure, the surfaces 49 of increased lead at the
opposite sides of all of the projections may then be formed by a final
cutting operation in which the rate of axial advancement of element 87 per
revolution is alternately increased and decreased as represented by broken
lines 100 of FIG. 15. As a further possible variation, this process in
which surfaces 49 are formed, by an oscillating or waving motion, may
itself be the first step of the procedure, with the opposite flank
surfaces 297 and 197 (or 59, 60, 61 etc.) at the trailing sides of the
projections being formed subsequently either in one or two steps as
desired.
As a further variation, it is contemplated that during the intervals when
cutter 87 is cutting the left flank surfaces 197 and 297 of projections
21a through. 21h, (or left flank surfaces 59, 60, 61 etc. of the FIG. 10
form), cutter 87 may be advanced axially at a rate slightly less than that
associated with the pitch p of FIG. 3, to give the flank surfaces at 197
and 297 (or 59, 60, 61 etc.) a lead angle slightly less than that
associated with pitch p, as represented somewhat diagrammatically by the
surface 48 of FIG. 7, thus assuring a proper cutting action by the edge 30
of each projection. This effect can be attained by alternately increasing
and decreasing the rate of axial advancement of cutter 87 in a manner
similar to that discussed in detail above in connection with surfaces 49
of FIG. 15. Thus, the broken lines 99 of FIG. 15 may have a waving
configuration similar to but the opposite of the waving configuration of
lines 100.
The outer conically tapered surfaces 32 (FIG. 3) of pre-forming projections
21c through 21h may be formed on those projections by machining body 83
conically either before or after the various cutting projections have been
formed, or at any intermediate point in the process. Also, the axial
recesses 22 in the tool (see FIG. 2) may be formed in body 83 before the
projections are formed, after they have been formed, or at any other
point.
To describe somewhat more specifically a particular presently preferred two
step process for producing the arrangement of FIG. 10, the cutter 87 may
in one of the two steps of that process form all of the right side flank
surfaces of all of the projections 58a through 58h, and in the other step
form all of the left side flank surfaces of all of the projections. The
two steps may be performed in either order, that is, with either step
first, and each step may include a series of progressively deepening cuts.
During each of these cuts, the cutter advances from right to left, to
successively form surfaces on projections 58h, 58g, etc. through 58a.
During each cut in forming the right hand flank surfaces, the rate of axial
advancement of the cutter per revolution is alternately slightly increased
and slightly decreased to follow the waving line 100 of FIG. 15, and
thereby produce the surfaces 49 of FIGS. 7 and 15 on each of the
projections. The variation in the rate of advancement is such as to give
the surface 49 of each projection a lead angle slightly greater than the
maximum lead angle at which the tool body 57 and its projections are to be
advanced relative to a nut body 12 during a threading operation, that is,
the maximum lead angle of the thread formed in the nut body. During each
cut in forming the left hand flank surfaces, the rate of axial advancement
of the cutter relative to the nut body may be considered as varying in
accordance with the summation of two components as follows. As a first of
these components, the cutter may be considered as advancing at a basic
rate slightly greater than that corresponding to pitch p, to shift
surfaces 59, 60 etc. gradually leftwardly as illustrated in FIG. 10, with
the basic rate of advancement being reduced to a rate equaling that of
pitch p in forming the left flank surfaces of the final two projections
(21a and 21b of FIG. 3). Superimposed on this basic rate of advancement,
the second component may introduce a slight oscillation alternately
gradually increasing and decreasing the rate of advancement, to slightly
reduce the lead angle of the left flank surfaces as represented by the
angularity of surface 48 of FIG. 7. This variation in the rate of
advancement is such as to give the surface 48 at the left side of each
projection a lead angle slightly less than the minimum lead angle at which
the tool body and its projections move relative to the nut body during a
threading operation, and the resultant minimum lead angle of the formed
groove in the nut body. As a result of the converging angularity of
surfaces 48 and 49 of all of the projections, those surfaces are, during a
threading operation, always relieved slightly away from the thread flank
surfaces being cut by edges 30 and 31, so that only those edges engage the
material of the nut, in a manner enabling the edges to make optimum cuts
in the nut body.
While certain specific embodiments of the present invention have been
disclosed as typical, the invention is not limited to these particular
forms, but rather is applicable broadly to all such variations as fall
within the scope of the appended claims. For example, the teachings of the
invention may be applied to formation of a thread which varies in pitch in
accordance with any desired pattern of change, not necessarily the
described simple uniform increase in pitch. The invention may also produce
an external rather than internal thread of increasing or otherwise varying
pitch, by a die having cutting edges similar to those illustrated in FIG.
3 or others of the figures but projecting radially inwardly to form the
external thread. It is also contemplated that the thread forming
projections or portions of the tools embodying the invention may in some
instances be designed to forceably deform or reshape the material of the
work piece to the desired configuration of a thread and groove of varying
pitch without actually cutting the material and in a manner similar to a
thread rolling operation.
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